This invention relates to an amplifier with automatic gain control.
U.S. Pat. No. 4,079,199 describes an automatically controlled amplifier arrangement in which the gain is controlled depending on the occurrence of oscillations.
If in such an arrangement one or more microphones are connected to the inputs and one or more loudspeakers are connected to the output, oscillations may occur in the event of acoustic feedback between one or more of the loudspeakers and one or more of the microphones. Such a situation may occur when the arrangement is used for amplifying speech signals or music signals in an auditorium. The frequencies of the oscillations depend, inter alia, on the geometry of the auditorium, the temperature and relative humidity in the auditorium, the distance between the speaker and the microphone, and the number of listeners in the auditorium. Therefore, the oscillation frequencies are of a more or less stochastic nature. In order to counteract these oscillations it is proposed in U.S. Pat. No. 4,079,199 to detect random oscillations and subsequently to reduce the gain of the arrangement until the oscillations are eliminated. After a waiting period the gain of the arrangement is then increased again automatically. As a result of this, it is always possible that in the known arrangement random oscillations occur, for example because the characteristics of the auditorium have changed, for example when the number of listeners has increased or decreased. These oscillations (howling) are annoying to the audience.